1. Field of the Invention
The present invention relates to a bale press for agricultural harvest crops including a pressure channel having at least a portion of one of its sides formed by a pivotal rail section, a hydraulic cylinder for applying pressure to the rail section, a plunger displaceable in the pressure channel for compressing a harvest crop therein, and a control device for controlling operation of the bale press and including a load sensor for sensing loading of the plunger and means for changing the pressure applied to the rail section upon deviation of the sensing signal from a predetermined set value.
2. Description of the Prior Art
As known, the control of the loading arrangement of the pressing channel of a channel bale press substantially influences the pressure density of bales. Ejected bound bales exert, due to their drag resistance, a counter pressure in the outlet, width-adjustable section of the pressing channel the magnitude and density of which correspond to the newly-formed bales. The greater is the drag resistance the greater is the compression density of the new bales. Moist product or crop has a relatively greater resistance than a dry product, and it is, therefore, compressed to a greater extent, whereas with the dry product, bales with a substantially smaller density are produced if the cross-sectional size of the pressing channel opening is not controlled, i.e., is not changed in accordance with the nature of the crop. Because the degree of dryness, e.g., of a pressed lay rapidly and continuously changes during the day, in order to form bales with a uniform compression density, it was proposed to automatically control the size of the pressing channel opening in accordance with the characteristics of the pressed crop. Thus, European Patent No. 389,322 discloses means for using the force applied by the plunger or the reaction force of the plunger for controlling pressure in the pressure conduit leading to the loading arrangement of the pressing channel which sometimes is called bale channel. The pressure is controlled in such a manner that the force applied by the plunger remains constant. However, the device disclosed in the above-mentioned European patent has a number of drawbacks.
Specifically, the degree of compression of bales of the same material and moisture content is substantially different when the bales are produced in bale presses with different throughputs. Because the bales are produced with a control designed to prevent that the set force value is exceeded, the pressure in the pressure conduit can be reduced though the counter pressure in the pressing channel has not increased, and the friction forces remain unchanged when the same material is processed. During the measurement of the reaction forces of the plunger exerted on an eccentric main drive, it was determined that larger packages of the same material give rise to pressure force peaks in crank positions with a larger operational lever arm, and the pressure is reduced relatively to a greater extent.
The force peaks, which are observed during cutting of packages with different moisture contents and/or having a greater size, and during each plunger stroke or during delivery of heaps, lead to an undesirably large pressure reduction.
Further, the set pressure value of the pressure exerted on the pressing channel loading device, which is preset on the pressure limiting valve, cannot be automatically changed dependent on the plunger force.
Therefore, the bales, which are produced with the above-described constant pressure force control, do not have the density which can be achieved by an optimal operation of a bale press. Thus, e.g., if during pressing of moist straw in the morning, an optimal pressure force is established, this force is not automatically adjusted for producing bales with a corresponding rigidity in the afternoon when a drier straw is being processed. Therefore, the required pressure force is set manually which is expensive and does not permit to set an optimal pressure force in accordance with the actual data, as the operator, for safety sake, set this force below the optimal value in order to prevent clogging.
In the known large channel bale press model D-6000 of the assignee herein, the application of pressure to the pressing channel loading device is effected with a hydraulic cylinder, with the control being effected by using a pressure sensor. The hydraulic pressure to the hydraulic cylinder is controlled by using a pressure limiting valve the operation of which is controlled by a constant pressure control device. The pressure in the pressure conduit is reduced when it exceeds a predetermined set pressure value, and is increased when the pressure in the pressure conduit is below a set value. This type of control permits to obtain a uniform constant hydraulic pressure when the press operates with an oscillating changing pressure force. Accordingly, the same relatively high compression densities of bales can be obtained as with the pressure force control. The drawback of this control consists in that the pressure sensors senses not the compression of the product in the pressing channel or the movement resistance in the pressure channel but rather the hydraulic pressure applied in the direction transverse to the extent of the pressuring channel, to the adjustable rail section of the pressing channel, which results in overcompression or undercompression of bales dependent on whether the hydraulic pressure is above or below the set value. That is, with this type of control, the plunger force increases e.g., upon the delivery of heaps of swath products. The hydraulic pressure is only then adjusted, i.e., the compression deviation is only then eliminated when it is sensed on the unbound ejected bales which, in an unfavorable case, can amount to a time lag of 20 seconds between the occurrence of the deviation and its measurement. In this bale press, a safety coupling is provided for preventing drive overloading.
An object of the present invention is to eliminate the drawbacks of the prior art bale press control systems.
Another object of the present invention is to provide a bale press with a control device which insures a better adaptation of the control to different material characteristics to produce bales with optimal characteristics with an optimal operation of the bale press.
A further object of the present invention is to provide a bale press which would permit to produce bales with a maximal pressure density without overloading of the press.